Depressions of superfluid density and transition temperature of3he confined in small pores

Chainer, Timothy; Morii, Yukio; Kojima, H.

doi:10.1007/bf00683453

Cited by 23 publications

(8 citation statements)

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“…2 increases by 11% at all pressures. The present results are consistent with the healing length calculated from the measured depression of transition temperature from the bulk value in an array of small pores in a Nuclepore filter, 20 packed powders, 10 and a single submicron channel. 21 Although Eq.…”

Section: Ips/p) =*L\\ ~K$(t)/r](p Sb /P)[ap{r)/ar]andrsupporting

confidence: 90%

“…The fourthsound resonance techniques used to measure the superfluid density have been described in detail elsewhere. 10 Three fourth-sound cylindrical resonator cavities (length = 14 mm and diameter =8 mm), A, B, and C, packed with alumina powders 11 of nominal grain sizes, 3, 1, and 0.3 ^m, respectively, were all immersed in a chamber filled with liquid 3 He which was cooled by a cooper nuclear demagnetization apparatus. The temperature was measured from the magnetic susceptibility of a Lanthanum-doped cerium magnesium nitrate pill immersed also in the liquid with good thermal contact to the resonators.…”

mentioning

confidence: 99%

“…The relatively high Q at low temperature was unexpected from the rather small Q observed near the transition temperature by Chainer, Morii, and Kojima. 10 The Q measurements are relevant to the hydrodynamic boundary conditions on the normal fluid flow in restricted geometries, which is of current interest in its own right. 14 This will be discussed in a separate report.…”

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confidence: 99%

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Healing Length of SuperfluidHe3

Ichikawa¹,

Yamasaki²,

Akimoto³

et al. 1987

Phys. Rev. Lett.

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Using fourth-sound techniques, we have measured the depression of the superfluid fraction of 3 He confined in small pores of packed powder over wide temperature (0.2 < T/T c <1) and pressure (0.5 < p < 20 bars) ranges. From the analysis of the data we determine the magnitude and the pressure dependence of the healing length. The healing length decreases from 520 A at 0.5 bar to 200 A at 20 bars. The values are in fair agreement with those expected from the BCS expression.PACS numbers: 67.50.Fi, 74.50.-l-r When a superfluid is confined in a sufficiently restricted geometry, the macroscopic order parameter describing the superfluid state becomes distorted by the presence of the boundary wall. 1 " 3 The nature of distortion will be determined by the particular boundary conditions that the wall imposes on the order-parameter function. Theoretical and experimental studies aimed at probing the boundary conditions for superfluid 3 He are currently under active research. 4 Understanding that the boundary conditions will be important in the design of an appropriate weak link for observing the long-sought analog of the Josephson effect in superfluid 3 He. 5 ' 6 Interpretation of experiments on superfluid-3 He films will be related to the boundary conditions. An important parameter in these phenomena is the healing length which determines the characteristic distance over which the order parameter decreases from its bulk value to zero near a wall. In this paper we describe a systematic determination of the healing length over a wide pressure range from the analysis of the measured superfluid fraction of 3 He confined in the pores of packed powder.Ambegaokar, de Gennes, and Rainer 1 showed that the nature of scattering of quasiparticles at a solid wall plays a crucial role in the determination of the boundary conditions. If the scattering is completely diffusive, they showed that the perpendicular (to the wall surface) component of the order parameter vanishes at the wall and that the parallel component is depressed from the bulk value by a factor of ~£O/£(JT). Here £n is the zerotemperature coherence length and %(T) is the temperature-dependent healing length. Recently, Buchholtz 7 showed that if the surface is bumpy at random on the scale of inverse Fermi wave number (~5 A) the parallel component also vanishes at the surface. It seems reasonable to assume that the powder used in our experiment presents diffuse scattering surfaces and that all components of the order parameter vanish at the surface.The Ginsburg-Landau (GL) equations, including the gradient terms for superfluid 3 He, have been derived by Ambegaokar, de Gennes, and Rainer. ] The GL equations define a natural length scale given by the healing length for the spatial variation of the order parameter. Minimizing the GL free-energy functional by variational calculation, Ebisawa and Arai 8 have shown that if a cylindrical pore of radius R is filled with superfluid 3 He-Z? whose order parameter obeys the above boundary conditions, the average superfluid density in th...

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Section: Ips/p) =*L\\ ~K$(t)/r](p Sb /P)[ap{r)/ar]andrsupporting

confidence: 90%

mentioning

confidence: 99%

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confidence: 99%

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Healing Length of SuperfluidHe3

Ichikawa¹,

Yamasaki²,

Akimoto³

et al. 1987

Phys. Rev. Lett.

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“…The breaking of superfluid pairs of 3 He by a diffusely scattering surface produces a reduction in superfluid density and transition temperature which were predicted [1,2] and observed in a number of experiments [3][4][5][6][7][8]. Freeman et ai [7] observed that the transition temperature and superfluid fraction were restored to bulk values by the addition of 4 He, as is expected for a specularly scattering surface.…”

Section: Laboratory Of Atomic and Solid State Physics Cornell Universimentioning

confidence: 79%

Hysteretic solidification of surfaceHe4measured by the modification of the specularity of
Sm
¹
,
Jm
²

1992
Phys. Rev. Lett.
35
1
15
0
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We have measured the superfluid fraction of 3 He in pores of sintered silver. The superfluid fraction, which is suppressed by confinement, increases with pressure due to the decreasing coherence length. Coating the surfaces with a thin film of 4 He partially restores the suppressed superfluidity, but above 17 bars this effect diminishes as the 4 He film solidifies. This solidification occurs over a range of about 9 bars and is hysteretic. With a slightly thicker 4 He film, solidification occurs at pressures greater than that required for bulk (25 bars).PACS numbers: 67.50.Fi, 67.40.Hf This Letter describes a series of experiments on 4 He and 3 He confined within the pores of sintered silver. The 3 He functions as both a hydrostatic medium to generate pressure as well as a detector of specular scattering of 3 He quasiparticles at the surfaces. The 4 He, which is preferentially plated onto the surfaces, serves as the agent to induce specularity as well as the material whose solidification is studied in this experiment.The breaking of superfluid pairs of 3 He by a diffusely scattering surface produces a reduction in superfluid density and transition temperature which were predicted [1,2] and observed in a number of experiments [3][4][5][6][7][8]. Freeman et ai [7] observed that the transition temperature and superfluid fraction were restored to bulk values by the addition of 4 He, as is expected for a specularly scattering surface. Kim et ai [8] also saw an increase in the superfluid fraction of 3 He in a porous medium formed from //m-sized particles following the addition of 4 He. In the normal fluid, Tholen and Parpia [9] induced slip, which is associated with specular scattering, by the addition of similar coverages of 4 He to the surfaces.One of the outstanding questions is whether the conversion of the 4 He fluid layer to a solid reduces the specularity. We find that solidification does destroy the specularity of the interface, and this destruction of specularity is used in this experiment to indicate the phase of the surface 4 He. The process of solidification occurs over a range of pressures starting below 25 bars, and is strongly dependent on the 4 He film thickness.In this experiment, the 3 He was confined in a region with pore sizes comparable to the coherence length in the superfluid. The expected diffuse scattering of 3 He should break pairs and suppress the total superfluid fraction below the bulk value. Specular scattering induced by a surface layer of 4 He is expected to reduce or eliminate this suppression. By measuring the superfluid fraction following a change in pressure, we can determine the dependence of the specularity on the phase of the 4 He surface layer.The experiments were carried out in a torsion oscillator cell which contained a 0.75-cm-diam 0.75-cm-tall cylindrical plug of silver powder (nominal diameter of 700 A) sintered to 68% of solid density, with a 0.75-mm-diam hole drilled down the length of the sinter to promote thermal equilibrium. The cell was located in close proximity to an ...

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“…1 the experimental magneticfield, the resonator is made from silver, which has much lower nuclear heat capacity than copper or copper-containing alloys. Although epoxy--used by Chainer et al 11 for their resonators--would also serve well in this respect, fabricating the resonator from metal reduces capacitive coupling between the receiver and driver and allows easy disassembly. The dimensions of the cylindrical resonator are: length 12.7 ram, outside diameter 12.7 mm, and inside diameter 6.3 ram.…”

Section: Fourth Sound Resonatormentioning

confidence: 99%

The effect of a magnetic field on fourth sound in 3He

Daly

1988

J Low Temp Phys

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The influence of a magnetic field on the propagation o f fourth sound in superfluid 3He is studied. The field and temperature dependences of the average superfluid density Ps/ P and fourth sound Q are measured. The field dependence Of ~s/ p is very different in a porous medium than predicted by Ginzburg-Landau theory applied to bulk liquid. In particular, a magnetic suppression of ~s/ p is observed in the temperature and pressure ranges corresponding to the A phase in bulk liquid. There is strong evidence of a magnetic suppression of T c itself. The measured ps/ P has a slight history dependence in a magnetic feld, but none in zero field. The fourth-sound Q values are compared to the theoretical work of Smith, Jensen, and Wolfle. Quantitative confirmation of their work is problematic.

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Depressions of superfluid density and transition temperature of3he confined in small pores

Cited by 23 publications

References 38 publications

Healing Length of SuperfluidHe3

Healing Length of SuperfluidHe3

Hysteretic solidification of surfaceHe4measured by the modification of the specularity of
Sm
¹
,
Jm
²

1992
Phys. Rev. Lett.
35
1
15
0
View full text Add to dashboard Cite

The effect of a magnetic field on fourth sound in 3He

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Depressions of superfluid density and transition temperature of3he confined in small pores

Cited by 23 publications

References 38 publications

Healing Length of SuperfluidHe3

Healing Length of SuperfluidHe3

Hysteretic solidification of surfaceHe4measured by the modification of the specularity ofSm1, Jm2 1992Phys. Rev. Lett.351150View full textAdd to dashboardCite

The effect of a magnetic field on fourth sound in 3He

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About

Hysteretic solidification of surfaceHe4measured by the modification of the specularity of
Sm
¹
,
Jm
²

1992
Phys. Rev. Lett.
35
1
15
0
View full text Add to dashboard Cite